CVE-2026-74513 (GCVE-0-2026-74513)

Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-08-17 05:48
VLAI
Title
dibs: fix use-after-free of dmb_node in loopback attach/detach/unregister
Summary
In the Linux kernel, the following vulnerability has been resolved: dibs: fix use-after-free of dmb_node in loopback attach/detach/unregister dibs_lo_attach_dmb(), dibs_lo_detach_dmb() and dibs_lo_unregister_dmb() look up the dmb_node under dmb_ht_lock, drop the lock and only then operate on the node's refcount. Nothing keeps the node alive across that window: __dibs_lo_unregister_dmb() removes the node from the hash table under the write lock and immediately frees it. A concurrent final put can therefore free the node between the lookup and the refcount operation: CPU0 (attach) CPU1 (owner unregisters) read_lock_bh(&dmb_ht_lock) find dmb_node (refcnt == 1) read_unlock_bh(&dmb_ht_lock) refcount_dec_and_test() 1 -> 0 write_lock_bh(&dmb_ht_lock) hash_del(&dmb_node->list) write_unlock_bh(&dmb_ht_lock) kfree(dmb_node) refcount_inc_not_zero(&dmb_node->refcnt) <-- use-after-free The same window exists for the refcount_dec_and_test() calls in the detach and unregister paths. Close the race structurally by making hash table membership and the refcount transitions atomic with respect to each other: - Perform the final refcount_dec_and_test() and hash_del() in a single dmb_ht_lock write-side critical section, in both the unregister and the detach path. Freeing the node still happens after the lock is dropped, which is safe because a node whose refcount reached zero has left the hash table and can no longer be found. - This establishes the invariant that any node found in the hash table holds at least one reference, and that the final reference can only be dropped under the write lock. dibs_lo_attach_dmb() can thus take its reference with a plain refcount_inc() while still holding the read lock; refcount_inc_not_zero() is no longer needed. __dibs_lo_unregister_dmb() no longer touches the hash table and is renamed to dibs_lo_free_dmb() accordingly. Note: commit cc21191b584c ("dibs: Move data path to dibs layer") moved the code to its current location; the race was introduced earlier by commit c3a910f2380f ("net/smc: implement DMB-merged operations of loopback-ism"). Tested SMC-D via ISM and dibs loopback.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6994 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: c3a910f2380fe294d14e42af66af3d3eed8fecbf , < c0837aeace96152d14b17fdd19d70102b6631a7d (git)
Affected: c3a910f2380fe294d14e42af66af3d3eed8fecbf , < 48c073f88c93707089a4214f21cb4c3de5aea6e4 (git)
Affected: c3a910f2380fe294d14e42af66af3d3eed8fecbf , < a10ea943356b9d70c5616a0a06f6fa97cfdaccb1 (git)
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Linux Linux Affected: 6.10
Unaffected: 0 , < 6.10 (semver)
Unaffected: 6.18.44 , ≤ 6.18.* (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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Show details on NVD website
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{
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          "product": "Linux",
          "programFiles": [
            "drivers/dibs/dibs_loopback.c"
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          "vendor": "Linux",
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ndibs: fix use-after-free of dmb_node in loopback attach/detach/unregister\n\ndibs_lo_attach_dmb(), dibs_lo_detach_dmb() and dibs_lo_unregister_dmb()\nlook up the dmb_node under dmb_ht_lock, drop the lock and only then\noperate on the node\u0027s refcount. Nothing keeps the node alive across\nthat window: __dibs_lo_unregister_dmb() removes the node from the hash\ntable under the write lock and immediately frees it.\n\nA concurrent final put can therefore free the node between the lookup\nand the refcount operation:\n\nCPU0 (attach)                     CPU1 (owner unregisters)\n\nread_lock_bh(\u0026dmb_ht_lock)\nfind dmb_node (refcnt == 1)\nread_unlock_bh(\u0026dmb_ht_lock)\n                                  refcount_dec_and_test() 1 -\u003e 0\n                                  write_lock_bh(\u0026dmb_ht_lock)\n                                  hash_del(\u0026dmb_node-\u003elist)\n                                  write_unlock_bh(\u0026dmb_ht_lock)\n                                  kfree(dmb_node)\nrefcount_inc_not_zero(\u0026dmb_node-\u003erefcnt)  \u003c-- use-after-free\n\nThe same window exists for the refcount_dec_and_test() calls in the\ndetach and unregister paths.\n\nClose the race structurally by making hash table membership and the\nrefcount transitions atomic with respect to each other:\n\n- Perform the final refcount_dec_and_test() and hash_del() in a single\n  dmb_ht_lock write-side critical section, in both the unregister and\n  the detach path. Freeing the node still happens after the lock is\n  dropped, which is safe because a node whose refcount reached zero has\n  left the hash table and can no longer be found.\n\n- This establishes the invariant that any node found in the hash table\n  holds at least one reference, and that the final reference can only\n  be dropped under the write lock. dibs_lo_attach_dmb() can thus take\n  its reference with a plain refcount_inc() while still holding the\n  read lock; refcount_inc_not_zero() is no longer needed.\n\n__dibs_lo_unregister_dmb() no longer touches the hash table and is\nrenamed to dibs_lo_free_dmb() accordingly.\n\nNote: commit cc21191b584c (\"dibs: Move data path to dibs layer\") moved\nthe code to its current location; the race was introduced earlier by\ncommit c3a910f2380f (\"net/smc: implement DMB-merged operations of\nloopback-ism\").\n\nTested SMC-D via ISM and dibs loopback."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "lang": "en",
              "value": "AV:L - The bug is only in the DIBS loopback driver used for same-host SMC-D DMB merge; reachable via AF_SMC connect/accept/close syscalls, not from remote packet handling, and loopback-ism cannot be used across machines.\nAC:L - This is a refcount/hash-table race where an attacker can open multiple SMC loopback connections and concurrently trigger attach, detach, and unregister to control both sides of the window without external timing dependencies.\nPR:L - No capability checks gate AF_SMC socket create/connect/close; any unprivileged local user (including in a user/network namespace with SMC/DIBS loopback enabled) can drive the vulnerable dibs_lo_attach/detach/unregister paths.\nUI:N - Exploitation requires only attacker-controlled SMC socket operations; no victim interaction such as opening files, mounting filesystems, or approving prompts is needed beyond normal daemon availability.\nS:U - Impact is confined to kernel memory corruption and privilege escalation within the same kernel security boundary; this is not a VM escape, IOMMU bypass, or cross-authority sandbox breakout.\nC:H - Use-after-free on dibs_lo_dmb_node allows operating on freed slab memory; attach then returns cpu_addr/len from the freed node, enabling arbitrary kernel memory disclosure via heap reuse.\nI:H - The UAF permits corrupting refcount and adjacent heap metadata and returning a dangling buffer pointer used as a merged SMC send buffer, enabling arbitrary kernel writes and potential code execution.\nA:H - Concurrent refcount operations on a freed dmb_node can cause kernel oops/panic from invalid refcount access or use of freed folio-backed memory during SMC-D buffer attach/detach teardown."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:48:04.292Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        },
        {
          "url": "https://git.kernel.org/stable/c/48c073f88c93707089a4214f21cb4c3de5aea6e4"
        },
        {
          "url": "https://git.kernel.org/stable/c/a10ea943356b9d70c5616a0a06f6fa97cfdaccb1"
        }
      ],
      "title": "dibs: fix use-after-free of dmb_node in loopback attach/detach/unregister",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74513",
    "datePublished": "2026-08-15T12:27:34.329Z",
    "dateReserved": "2026-08-15T05:44:03.909Z",
    "dateUpdated": "2026-08-17T05:48:04.292Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
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      "date": "2026-10-19",
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      "percentile": "0.01905"
    },
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                "product": "Linux",
                "programFiles": [
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ndibs: fix use-after-free of dmb_node in loopback attach/detach/unregister\n\ndibs_lo_attach_dmb(), dibs_lo_detach_dmb() and dibs_lo_unregister_dmb()\nlook up the dmb_node under dmb_ht_lock, drop the lock and only then\noperate on the node\u0027s refcount. Nothing keeps the node alive across\nthat window: __dibs_lo_unregister_dmb() removes the node from the hash\ntable under the write lock and immediately frees it.\n\nA concurrent final put can therefore free the node between the lookup\nand the refcount operation:\n\nCPU0 (attach)                     CPU1 (owner unregisters)\n\nread_lock_bh(\u0026dmb_ht_lock)\nfind dmb_node (refcnt == 1)\nread_unlock_bh(\u0026dmb_ht_lock)\n                                  refcount_dec_and_test() 1 -\u003e 0\n                                  write_lock_bh(\u0026dmb_ht_lock)\n                                  hash_del(\u0026dmb_node-\u003elist)\n                                  write_unlock_bh(\u0026dmb_ht_lock)\n                                  kfree(dmb_node)\nrefcount_inc_not_zero(\u0026dmb_node-\u003erefcnt)  \u003c-- use-after-free\n\nThe same window exists for the refcount_dec_and_test() calls in the\ndetach and unregister paths.\n\nClose the race structurally by making hash table membership and the\nrefcount transitions atomic with respect to each other:\n\n- Perform the final refcount_dec_and_test() and hash_del() in a single\n  dmb_ht_lock write-side critical section, in both the unregister and\n  the detach path. Freeing the node still happens after the lock is\n  dropped, which is safe because a node whose refcount reached zero has\n  left the hash table and can no longer be found.\n\n- This establishes the invariant that any node found in the hash table\n  holds at least one reference, and that the final reference can only\n  be dropped under the write lock. dibs_lo_attach_dmb() can thus take\n  its reference with a plain refcount_inc() while still holding the\n  read lock; refcount_inc_not_zero() is no longer needed.\n\n__dibs_lo_unregister_dmb() no longer touches the hash table and is\nrenamed to dibs_lo_free_dmb() accordingly.\n\nNote: commit cc21191b584c (\"dibs: Move data path to dibs layer\") moved\nthe code to its current location; the race was introduced earlier by\ncommit c3a910f2380f (\"net/smc: implement DMB-merged operations of\nloopback-ism\").\n\nTested SMC-D via ISM and dibs loopback."
          }
        ],
        "id": "CVE-2026-74513",
        "lastModified": "2026-08-17T06:19:48.007",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
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              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
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        "published": "2026-08-15T13:17:56.410",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/48c073f88c93707089a4214f21cb4c3de5aea6e4"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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          },
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          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-19T17:41:46+00:00",
      "cve": "CVE-2026-74513",
      "id": "CVE-2026-74513",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: dibs: fix use-after-free of dmb_node in loopback attach/detach/unregister",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74513.json",
      "version": "3"
    }
  }
}



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